Merge array of objects with an object using Object.assign

Question

I'm trying to merge array of objects which with an object using Object.assign()

var state = {
    items: [{
       id: "Harko",
       name: "Haris"
    },
    {
      id: "Benko",
      name: "Benjo"
    }]

}

var a = {
    id: "Benko",
    name: "Bengalka"
}

What I tried already:

Object.assign(state.items,a);
Object.assign({}, { items: [state.items,a]);

What I want to get is the following:

{
    items: [{
       id: "Harko",
       name: "Haris"
    },
    {
      id: "Benko",
      name: "Bengalka"
    }]
}

So I want that Object in var state with id "Benko" to be overwritten by var a, because they have same id.

Is this possible with Object.assign?

CodingIntrigue · Accepted Answer · 2016-11-04 10:47:35Z

8

You can't really do that at a top-level using Object.assign. What you need to do is find the object reference first, then you can use Object.assign to update it's properties:

const state = {
    items: [{
       id: "Harko",
       name: "Haris"
    },
    {
      id: "Benko",
      name: "Benjo"
    }]

}

const a = {
    id: "Benko",
    name: "Bengalka"
}
const foundObject = state.items.find(obj => obj.id === a.id);
Object.assign(foundObject, a);
console.log(state);

answered Nov 4, 2016 at 10:47

CodingIntrigue

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Joseph Connolly · Accepted Answer · 2019-10-03 18:54:11Z

0

Lodash merge() worked for my use case:

let v = {foo: [{change: "first", leave: "here"}]}
_.merge(v, {foo: [{change: "second"}]})

Value of v after merge:

{ foo: [{change: "second", leave: "here"}]

Compare to Object.assign() which will replace the first item in the array with the second:

Object.assign(v, {foo: [{change: "second"}]})

Value of v after (leave prop is missing):

{ foo: [{change: "second"}] }

edited Oct 3, 2019 at 18:54

answered Oct 3, 2019 at 14:48

Joseph Connolly

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Johny Martin · Accepted Answer · 2022-03-15 14:48:10Z

0

In additional to Joseph Connolly answer: You can use mergeWith or assignWith methods from lodash with 3rd argument. Example from lodash docs:

function customizer(objValue, srcValue) {
  if (_.isArray(objValue)) {
    return objValue.concat(srcValue);
  }
}
 
var object = { 'a': [1], 'b': [2] };
var other = { 'a': [3], 'b': [4] };
 
_.mergeWith(object, other, customizer);
// => { 'a': [1, 3], 'b': [2, 4] }

answered Mar 15, 2022 at 14:48

Johny Martin

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